1. Field of the Invention
The invention relates to an actuator system and to a method of ensuring that at least one actuator in the actuator system cannot yield more than a maximum permissible force.
2. The Prior Art
For convenience, the disclosure of the invention will be based on patient lifters as disclosed e.g. in DE 199 50 689 A1 to Okin. The patient lifter comprises a frame provided with wheels and having a cantilever which is rotatable about a horizontal axis. A lifting sling for the patient may be secured at the end of the cantilever. Raising and lowering of the patient is performed by a linear actuator which is mounted on the frame and is connected with the cantilever. It is a safety requirement (standard EN1531) that patient lifters must not be capable of lifting more than one and one-half times the specified maximum load.
In order to meet this requirement in a simple manner in terms of costs and structure, it is turned to account that there is a direct relation between power consumption and load. Typically, a power cutout circuit is thus provided, which cuts out the power corresponding to one and one-half times the specified maximum load. This limit is preset by the manufacturer and can not be changed subsequently or only be changed with difficulty subsequently. However, the problem is that there is a great spread of the power necessary to lift a given load, which means that, in reality, the patient lifters can lift far more than the permissible load. It is not readily possible to limit the spread of the power in an acceptable manner.
The object of the invention is to provide an actuator system by means of which it may be ensured in a simple manner that the permissible load cannot be exceeded.